Summary and Terms

Terms

Phase: a homogeneous, chemically uniform, and physically distinguishable region of matter. Section 10.3.1

Phase Diagrams: Maps that relate a the conditions a material is under to the phases that it will exhibit. Section 10.3.3

Phase diagrams can be classified as unary, binary or ternary (or even further, which we typically use computers for) based on the number of components present. Components are parts of a system that act as distinct chemical elements. Section 10.4.2

Phase Fields: Two dimensional regions on a phase diagram that predict what equilibrium phases a material will exhibit under a given set of conditions. Section 10.4.2

Phase Boundaries: Lines at the edges of phase fields which describe where phase changes will occur - crossing them results in a new equilibrium phase. Section 10.4.2

Invariant Points: Points on phase diagrams where conditions cannot be varied while maintaining the same phase equilibrium. The triple point on the unary temperature-pressure phase diagram of water is a well known example. Section 10.4.2

Composition: The relative amount of a chemical component present in a system. We can describe composition is several ways, such as weight percent or atom percent, and it frequently appears on at least one phase diagram axis. Section 10.5.1

Solubility Limit: The point within a mixture where one phase can no longer accommodate more of a specific component, such as the point at which liquid water can dissolve no more sugar. Section 10.5.2

Isomorphous Binary Phase Diagram: A phase diagram which displays the relative concentration of two components having pure phases of the same crystal structure on one axis. Section 10.6.1

Liquidus: A phase boundary above which only a liquid phase is present. Section 10.6.4

Solidus: A phase boundary below which only a solid phase is present. Section 10.6.4

Tie Line: On a T-X diagram, an isothermal (same temperature) line that we use to determine both the relative amounts of each phase present at any point in a two phase region (based on the lever rule) and the composition of the two phases (based on where the line intersects phase boundaries). Section 10.6.8

Lever Rule: A method for determining how much of a given phase is present at a point in a two phase region, done by measuring the total length of a tie line, and dividing the length of one of the segments to the left or right of the particular point on the diagram by it. Section 10.6.14

Microstructure: The arrangement of microconstituents and phases within a material. Section 10.7.1

Microconstituents: Distinct and identifiable components of a material. These can be single, distinct phases or consistent arrangements of multiple phases. Section 10.7.1

Binary Eutectic Phase Diagram: A phase diagram featuring two components which do not mix well. These phase diagrams exhibit solidi and liquidi, but also eutectic points and phase separation at low temperatures unlike previously considered diagrams. Section 10.7.4

Eutectic Composition: Invariant points found in Binary Eutectic Phase Diagrams which lie at the boundary between a mixed-phase solid region and a single-phase liquid region. Eutectic compositions display lower freezing/melting temperatures than surrounding compositions and occur at Eutectic Temperatures. Section 10.7.4

Solvus: A type of phase boundary that describes the maximum solid solubility of a phase, or in other words, how much of a minority component the phase can accommodate without a changing. Section 10.7.6

Quasi-Equilibrium Cooling: An assumption that when we cool a material, its microstructures are allowed to reach their equilibrium states (the ones indicated by the equilibrium phase diagram) before further phase changes occur. This assumption allows us to predict microstructure without getting into the weeds of nucleation and growth theory. Section 10.8.2

Eutectic/Lamellar Microstructure: The "zebra skin"-like microstructure that forms when a material is cooled below its eutectic isotherm. Section 10.8.8

Hyper-/Hypoeutectics: Compositions that contain more or less of a component than the eutectic composition respectively. Which one is which depends on the component we put on the axis of a binary phase diagram. Section 10.8.11

Primary/Proeutectic: A label for phases in a binary eutectic phase diagram that solidify above the eutectic temperature. Section 10.8.13

Intermediate Phase Diagrams: More complex phase diagrams in which new phases emerge outside of the compositional extremes as in binary eutectic and isomorphous phase diagrams. Section 10.9.1

Line Compounds: Phases that exist only at one single composition, commonly seen with intermetallics where the atoms must adopt a strict compositional ratio. Section 10.9.2

Other Invariant Reaction Points: Points similar to eutectic points in that they transition cleanly from two phases to one or vice versa, but which involve different states, such as a liquid and solid cooling to form a single solid. See Section 10.9.4 for a detailed explanation.

Freezing/melting Transition: A point where a phase transitions from a liquid to a solid. Section 10.9.5

Polymorphic Transition: A point where a solid phase transitions to another solid phase. Section 10.9.5